The relevance of stem cells to cutaneous biology is only now beginning to be appreciated. Evidence now points to a pivotal role for stem cells in normal skin homeostasis, regeneration after injury, and in development of cutaneous neoplasms. Only now are protocols being developed for isolation and in vitro propagation of circulating stem cells being developed and characterized. The proposal will develop tools needed to routinely isolate and propagate circulating stem cells that are committed to endothelial cell differentiation. The function of these cells and their roles in inflammatory, regenerative and neoplastic processes in the skin is only now beginning to be appreciated. The tools and data to be developed in this proposal will allow for submission of a grant proposal to multiple outside sources. Specific aims: 1. To establish techniques for the growth of endothelial cells from peripheral blood stem cells in humans and to characterize the cells in regards to specific endothelial cell markers and growth characteristics. 2. To establish techniques for the growth of endothelial cells from bone marrow, fetal liver, embryonic stem cells, or peripheral blood stem cells in mice and to characterize the cells in regards to specific endothelial cell markers and growth characteristics.